Mass separation in an asymmetric channel

TL;DR

This paper introduces a mass separation mechanism in an asymmetric channel using entropic barriers and oscillatory forces, enabling the sorting of particles based on their mass with tunable parameters.

Contribution

It presents a novel mass sorting method leveraging entropic barriers and oscillatory forces, with an empirical relation for optimal particle mass.

Findings

Particles with an optimal mass drift faster under oscillatory force.

The optimal mass scales as (a*omega^2)^(-0.4).

Static bias can selectively direct lighter particles.

Abstract

We present a mechanism to sort out particles of different masses in an asymmetric channel, where the entropic barriers arise naturally and control the diffusion of these particles. When particles are subjected to an oscillatory force, with the scaled amplitude $a$ and frequency $\omega$, the mean particle velocity exhibits a bell-shaped behavior as a function of the particle mass, indicating that particles with an optimal mass $m_{op}$ drift faster than other particles. By tuning $a$ and $\omega$, we get an empirical relation to estimate $m_{op} \sim (a\,\omega^2)^{-0.4}$. An additional static bias, applied in the opposite direction of the rectified velocity, would push the particles of lighter mass to move in its direction while the others drift opposite to it. This study is useful to design lab-on-a-chip devices for separating particles of different masses.